Rapid phenotypic changes of reproductive traits in response to experimental modifications of spatial structure in Nile tilapia, Oreochromis niloticus

The reproductive characteristics of Oreochromis niloticus, a multiple spawn er, have been compared between populations submitted experimentally to thre e types of spatial structure. Fish from a same original stock were divided and reared for 2 months in: 1) concrete tanks with a bare bottom, 2) concre te tanks with a sandy bottom, or 3) concrete tanks equipped with an artific ial reef. The females were then killed and their gonads examined for sexual stage and fecundity determination. Fecundity was inversely correlated to t he spatial complexity of the environment whereas oocyte size tented to incr ease together with spatial complexity. Females placed in tanks with artific ial reefs presented a lower fecundity and reproductive investment and bigge r oocytes than those maintained in the bare bottom tanks. Fish reared in ta nks with a sandy bottom had intermediate reproductive traits. The response of females to changes in the spatial structure of their environment was obs erved after only one or two reproductive cycles, providing the first experi mental evidence of such rapid phenotypic adaptation to environmental comple xity. The results also indicate that the perception of living space, arisin g from the availability of refuges and spawning sites, is more likely to in fluence the reproduction of tilapias than substrate quality. (C) 2001 Ifrem er/CNRS/Inra/IRD/Cemagref/Editions scientifiques et medicales Elsevier SAS.